1. Field of the Invention
The present invention relates to a vibration unit, and more particularly to a vibration unit which is light-transmittable and flexible.
2. Description of the Related Art
As piezoelectric materials develops, the size regardless of volume or thickness of actuators including piezoelectric actuators, piezoelectric motors, ultrasonic motors, electrets or related thin actuators made of a piezoelectric material is minimized. Since the principle of piezoelectric effect (which is a prior art technology disclosed years ago, and thus will not be described here) is mainly divided into two types: direct piezoelectric effect and converse piezoelectric effect. If a pressure is applied to a piezoelectric body, then the electric dipole moment of the piezoelectric body will be compressed and shortened together with the material. Now, the resistance against the aforementioned tendency in the piezoelectric body will generate a voltage to maintain the original status of the piezoelectric body, and this effect is called direct piezoelectric effect. On the other hand, if an electric field is applied to the piezoelectric body, the electric dipole moment will be elongated, the piezoelectric body will be extended in the direction of the electric field to convert electric energy into mechanical energy, and this effect is called converse piezoelectric effect. The foregoing piezoelectric actuators and piezoelectric motors, etc are devices having the converse piezoelectric effect and capable of creating mechanical energy such as vibrational energy for producing vibrations.
There are two types of piezoelectric actuators divided according to their applications as follows.
The first type of piezoelectric actuators is to make use of a pure linear displacement of a longitudinal effect and a lateral effect created by the piezoelectric actuator, which the piezoelectric actuator is considered as a linear motor with a micro/nano scale micro-movement capability, whose structure includes a single-layer device, a multi-layer device and a tubular device, etc.
The second type of piezoelectric actuators is a complex curved displacement type capable of producing a relatively larger displacement, and such piezoelectric actuator is composed of a piezoelectric device and other elastic materials, and this type of piezoelectric actuators includes unimorph and bimorph.
The single-layer piezoelectric device comes with a simple structure but generates very small displacement quantity. The single-layer piezoelectric device generally has a thickness approximately ranging from 0.1 mm to 1 mm, and the displacement quantity approximately to 100 nm. In recent years, as the development of micro manufacturing technology of electromechanical systems (MEMS) advances, there is a trend of changing piezoelectric materials into thin films with a response frequency ranging from 100 MHz to several GHz. The way of driving a single-layer piezoelectric device is to apply a voltage in the direction of the thickness of the piezoelectric device, such that a polarization occurs inside the material to produce contractive and expansive deformations. Because the behavior of polarization process similar to the charges which are accumulated to the capacitor, so the piezoelectric device also has the property of a capacitor.
Basically, the multi-layer piezoelectric device is formed by stacking single-layer piezoelectric devices together with one another, and each layer is insulated by a thin film. Generally, the quantity of layers can be ranged from tens to hundreds of layers, so these single-layer piezoelectric devices have a larger displacement quantity ranging from several microns to tens of microns, and a natural frequency ranging from several kHz to 10 kHz. The energy conversion efficiency of the multi-layer piezoelectric device is also higher than that of the single-layer piezoelectric device. Each single-layer piezoelectric device is isolated by an electrode, and the polarization direction of each single-layer piezoelectric device is opposite to the polarization direction of an adjacent single-layer piezoelectric device. Although the mechanical structure is a serially connected structure, the electric property is of a parallel type. A voltage is applied to each single-layer piezoelectric device simultaneously for driving the device, such that the single-layer piezoelectric device can be shifted and changed in polarization direction.
In present existing technologies, the use of piezoelectric actuators, piezoelectric motors, ultrasonic motors, electret or related thin actuator is very popular. For example, a mini supersonic transducer of a flexible substrate as disclosed in TW Pat. Publication No. 575024 comprises: a substrate, made of a flexible material, and having a first surface and a second surface disposed on top and bottom sides of the first substrate respectively, wherein both sides of the first surface have a lead frame to constitute a support structure by flexibility; and a vibrating film, having a first surface and a second surface, wherein the second surface is disposed on a lead frame; and a plurality of first electrodes and second electrodes, wherein the first electrodes are disposed on the substrate, and the second electrodes are disposed on the vibrating film. With the aforementioned assembly, the conventional supersonic transducer can achieve the effects of simplifying the manufacturing procedure, increasing the deformation of the vibrating film and the effective sensing area between the driving and sensing electrodes, reducing the effect between impedance and a matched layer, increasing the detection sensitivity and enhancing the performance without incurring a higher cost. Although this published patent has disclosed a flexible supersonic transducer, yet the flexible supersonic transducer lacks of light-transmittably, and produces very limited vibrations for its application in a speaker. So the transducers of this sort cannot be used as a primary device for producing vibrations.
In addition, a no-bias analog resistive touch display panel as disclosed in TW Pat. No. I249708 comprises a core layer made of an electret material having a piezoelectric effect, a transparent conductive film layer formed on upper and lower surface of the core layer separately, a highly conductive metal electrode formed at each edge of the conductive film layer on one of the surfaces of the core layer, and a transmission line electrically coupled to the electrode and a controller. If the no-bias analog resistive touch display panel is touched, a potential difference will be produced between the conductive film layers of the upper and lower surfaces of the core layer by the piezoelectric effect of the electret. Since the distance between the touched point and each conductive metal electrode disposed on the conductive film layer varies, the impedance is different, so that each electrode generates a corresponding current signal according to the potential difference and impedance, and the transmission line electrically coupled to the electrode is provided for outputting the current signal to the controller for detecting position coordinates of the touched point after correction is made. Obviously, the aforementioned converse piezoelectric effect is applied in the aforementioned issued patent, wherein a transparent electret together with a potential sensing are used for the touch display panel. In the field and application of flexible touch display panels, the deformation rate generated by rolling the touch display panels will be different and a large quantity of electric potential energies will be produced, and thus the aforementioned invention cannot be applied to a primary device for producing vibrations.
As the development of the touch control technology advances, a purely touch control no longer can meet the user requirements anymore. When a general user operates a touch display panel, the user is limited by factors including the sensing sensitivity of the touch display panel, the response time of the operating system, and the different personal tactile sensing, and the user usually cannot determine instantly whether or not a touch operation is completed. To let users be able to immediately sense an end of a touch control action, some manufacturers connect the foregoing actuator to the bottom of a general touch display panel.
After a user touches the touch display panel by a touch object such as the user's hand or stylus, the actuator produces vibrations immediately, so that the user can sense the end of the touch action by the feedback of vibrations, and such feedback is called touch feedback or tactile feedback in present existing technologies.
It is expected that the actuator is limited by the properties of its material which the light cannot be penetrated through when the actuator is coupled to the touch display panel, the actuator cannot be installed only at the bottom of the touch display panel in order to avoid blocking the screen displayed by the touch display panel. Before a vibration produced by the actuator is transmitted to the touch object such as the user's hand or stylus, vibration waves have to pass through the touch display panel and the display panel (wherein the touch panel generally has a layer of touch display panel and a layer of display panel installed at the bottom of the touch panel), and the vibrational force is absorbed substantially after the vibration waves pass through two layers of panels with different properties. As a result, the user cannot sense the touch feedback for sure.
Although the touch display panel with the design of a touch feedback allows users to know about the completion of a touch control action, users need healthy eyes to operate such display panel, but users with a visual impairment such as blind people or cataract patients are unable to use such touch display panel.